Electron Cyclotron Resonance Propulsion

Abstract

The present invention relates to a satellite propulsion device (10) employing electron cyclotron resonance and magnetic nozzles, the propulsion device extending at least partially along a longitudinal axis (X) and comprising an outer conductor (22) extending longitudinally along said axis and an ionization chamber (8), the outer conductor laterally bounding the ionization chamber and the ionization chamber including a circular lateral opening (24) having a diameter D, and further comprising a screen (6) arranged coaxially with the longitudinal axis (X), the screen (6) having a ratio of its maximum lateral dimension D' to D between 3 and 15 and including a portion made of insulating material (61) and / or a portion made of conductive material (62).

Description

[Technical Field]

[0001]

[0001] This description relates to electron cyclotron resonance propulsion systems. [Background technology]

[0002]

[0002] Artificial satellites require thrusters to maintain their position and make orbital and attitude corrections. Similarly, space probes for exploring the solar system are equipped with thrusters to maintain very precise positions around selected planets or to land on asteroids to collect material samples.

[0003]

[0003] Typically, these microthrusters generate thrusts of a few newtons or less. Chemical propulsion systems use liquid propellants such as hydrazine (N2H2) or hydrogen peroxide (oxygen-containing water). The decomposition of these propellants converts chemical energy into heat, which is then generated as thrust when the hot gases expand in a suitable nozzle. The material is ejected at high speed, generating a reaction force called thrust. This thrust is used to change the momentum of a spacecraft, probe, or satellite and influence its trajectory. One of the well-known limitations of these technologies is related to the ejection velocity that the gas can achieve. Furthermore, the mass of the propellant can reach a significant fraction of the total mass of the satellite, reducing the satellite's payload, which is a second limitation.

[0004]

[0004] However, by using electric and / or magnetic fields to accelerate ionized gas particles away from the propellant, it is possible to increase the propellant gas ejection velocity by several orders of magnitude. These so-called plasma thrusters enable missions to perform larger orbital maneuvers with the same amount of material, or equivalent maneuvers with less material payload. This allows for the reduction of satellite mass or the increase of payload capacity while keeping mass constant.

[0005]

[0005] With the increasing number of new satellites equipped solely with plasma thrusters, it is clear that these thrusters have great potential for application, but they present many technical challenges.

[0006]

[0006] For example, the first plasma propellants of the ECR (Electron Cyclotron Resonance) type that could be used in spacecraft had the drawback of being difficult to miniaturize, since they depended on the size of the coupling cavity that allowed the coupling of the plasma with the electromagnetic waves essential for plasma initiation. French Patent No. 1,162,545 proposes a miniaturized electron cyclotron resonance propulsion device that can initialize plasma by magneto-electron resonance (ECR) in a very small volume. This is achieved by a special arrangement of the ionized gas inlet, the magnetic field lines, and the electromagnetic wave coupling.

[0007] However, it is still desirable to improve the performance of such propulsion devices. Furthermore, problems remain regarding extending their service life. Problems remain with regard to erosion of components and wear due to plasma discharges. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] French Patent Invention No. 1162545 Summary of the Invention

[0009]

[0008] In this context, the object of the present invention is to provide a new electron cyclotron resonance propulsion system which does not have the above-mentioned drawbacks or which reduces some of these drawbacks.

[0010]

[0009] The present invention has as its particular object the provision of a particularly efficient electron cyclotron resonance thruster. One aspect of the invention is an electron cyclotron resonance thruster extending at least partially along a longitudinal axis, the electron cyclotron resonance thruster comprising an outer conductor and an ionization chamber, the outer conductor and the ionization chamber extending longitudinally along the axis, the outer conductor laterally bounding the ionization chamber, the ionization chamber having a circular lateral opening 24 having a diameter D, characterized in that the ionization chamber further comprises a screen arranged coaxially with the longitudinal axis, the screen having a maximum lateral dimension D', the ratio of D' to D being between 3 and 15. The screen includes portions made of insulating material and / or portions made of conductive material.

[0011] The present invention allows for a significant improvement in thruster performance. The thrust generated by such a thruster is increased by a factor of 1.3 compared to conventional plasma thrusters. The efficiency of the entire system (the ratio of the power contained in the plasma jet to the power supplied to the thruster) is increased by a factor of 1.7 compared to conventional plasma thrusters. When the thruster operates and ejects a plasma consisting of ions and electrons, the coaxial screen prevents electrons trapped by the most divergent magnetic field lines from coming into contact with thruster components. As a result, these divergent electrons, instead of being collected as an electric current by the thruster, accumulate near the screen, creating a local negative electric charge. This repels other divergent electrons and thus redirects them into the emitted particle beam. The plasma flow emitted by the thruster is thus increased.

[0012] In one embodiment of the present invention, the portion made of insulating material covers the portion made of conductive material. In one embodiment of the present invention, the portion made of insulating material completely covers the portion made of conductive material. In one embodiment of the present invention, the portion made of insulating material completely covers the portion made of conductive material, and the outer surface of the screen is made of insulating material.

[0013]

[0012] In another aspect of the present invention, the screen is attached to the outer conductor. In another aspect of the present invention, the propulsion device includes a magnetic field source, and the screen is attached to the magnetic field source. According to another aspect of the present invention, the propulsion device includes a body, and the screen is attached to the body. According to another aspect of the present invention, the propulsion device includes a magnetic field source and a body, and the screen is attached between the magnetic field source and the body. According to one aspect of the present invention, the screen is attached by screws made of insulating material.

[0014] In one aspect of the invention, the section made of insulating material is configured to electrically insulate the section made of conductive material from the outer conductor. In another aspect of the invention, the section made of insulating material is configured to electrically insulate the section made of conductive material from the remainder of the propulsion device. In this variation, the remainder of the propulsion device includes all elements of the propulsion device except for the screen.

[0015] In another aspect of the invention, the propulsion device further includes an element of insulating material configured to electrically insulate the screen from the outer conductor.

[0016]

[0015] In one variation, the portion made of conductive material covers the portion made of insulating material. In one aspect of the invention, the portion made of conductive material completely covers the portion made of insulating material. In one aspect of the invention, the portion made of conductive material is configured to completely cover the portion made of insulating material, whereby the outer surface of the screen is made of conductive material.

[0017]

[0016] In one aspect of the present invention, the portion made of conductive material has a polarity different from that of the outer conductor or other elements of the propulsion device. In one aspect of the present invention, the portion made of conductive material has a polarity different from that of the outer conductor or other elements of the propulsion device except for the screen. In one embodiment of the present invention, the portion made of conductive material has a negative polarity with respect to the outer conductor or other elements of the propulsion device. In one embodiment of the present invention, the portion made of conductive material has a negative polarity with respect to the outer conductor or other elements of the propulsion device except for the screen.

[0018] The present invention makes it possible to significantly improve the performance of a thruster. The thrust generated by such a thruster is amplified by a factor of more than 1.3 compared to conventional plasma thrusters. The total system efficiency, defined herein as the ratio of the power contained in the plasma jet to the power supplied to the thruster, is increased by a factor of more than 1.7 compared to conventional plasma thrusters. When the thruster is operating and a plasma consisting of ions and electrons is ejected, the negatively polarized coaxial screen pushes out electrons trapped in the most divergent magnetic field lines, thereby redirecting these divergent electrons into an ejected particle beam. This enhances the plasma flow ejected from the thruster.

[0019] In another aspect of the invention, the screen comprises a centrally concave disk or diverging shape, such as a truncated hollow cone or nozzle shape.

[0020]

[0019] In one aspect of the present invention, the outer conductor includes an inner wall made of graphite. In one aspect of the present invention, the outer conductor includes an inner wall that is generally cylindrical, and the inner wall is made of graphite. In one aspect of the present invention, the outer conductor is made of a conductive material, and includes an inner wall made of graphite. In one example, the outer conductor has a deposited layer of graphite on its inner wall. In another example, the outer conductor has a tube of graphite on its inner wall.

[0021]

[0020] Under the bombardment of plasma ions, graphite is less eroded than prior art materials such as aluminum. This extends the life of the outer conductor. Furthermore, plasma electrons striking the graphite inner wall of the outer conductor maintain good plasma containment with less electron re-emission due to secondary discharges, thereby avoiding energy loss from the plasma to the inner wall of the outer conductor. This significantly improves the performance of the thruster. The thrust generated by such a thruster increases by a factor of 1.6 compared to conventional plasma thrusters. The overall system efficiency (the ratio of the power contained in the plasma jet to the power supplied to the thruster) increases by a factor of 2.5 compared to conventional plasma thrusters.

[0022] In one embodiment of the present invention, the insulating material portion is made of a mixture of glass fiber and epoxy resin. In another embodiment of the present invention, the insulating material portion is made of a mixture of carbon fiber and epoxy resin. This composition makes it possible to realize a screen that is more rigid, lightweight, and thin.

[0023] In other embodiments, the insulating material portion is made of a Kapton® type resin or polyimide, or a ceramic such as alumina, boron nitride, or Macor® ceramic.

[0024] In one embodiment of the present invention, the portion made of insulating material is made of polyetheretherketone (PEEK) or polyetherketoneketone (PEKK).

[0025] In one embodiment of the present invention, the portion made of conductive material is, for example, a metal reinforcement material.

[0026] In one embodiment of the present invention, the portion made of conductive material is made of stainless steel, graphite, or aluminum.

[0027] In one embodiment of the present invention, the insulating portion is a film of insulating material, for example, a Kapton® type polyimide film.

[0028] In one embodiment of the present invention, the portion made of insulating material is a polymer-based paint layer, for example a paint layer based on polydimethylsiloxane (PDMS).

[0029] In one embodiment of the present invention, the thickness of the insulating material portion is between 200 nanometers and 1 millimeter. In one embodiment of the present invention, the thickness of the insulating material portion is greater than 1 micrometer.

[0030] In one embodiment of the present invention, the portion made of conductive material has a thickness of 200 nanometers to 1 millimeter. In one embodiment of the present invention, the portion made of conductive material has a thickness of more than 1 micrometer.

[0031]

[0030] A thickness greater than 1 micrometer improves the durability of the screen and resists erosion associated with the space environment.

[0032] In one embodiment of the present invention, the section of insulating material includes a resin reinforcement and a Kapton® type polyimide film.

[0033] In one embodiment of the present invention, the portion made of conductive material is joined to the portion made of insulating material.

[0034] In one embodiment of the present invention, the portion made of insulating material is joined to the portion made of conductive material.

[0035] In one embodiment, the outer conductor has inner and outer walls separated by a lateral thickness within which a homogenization chamber is formed, the homogenization chamber extending longitudinally through a portion of the outer conductor and having a generally hollow cylindrical shape. The homogenization chamber allows for uniform injection of gas circumferentially around the ionization chamber. The homogenization chamber allows for controlled injection of propellant gas.

[0036] In another aspect of the invention, the propulsion device includes gas injection means, said means including: at least one injection channel passing radially through the outer wall of the outer conductor and partially through the lateral thickness (223) of the outer conductor (222) and opening into the homogenization chamber; a homogenization chamber; - communication means configured so that the homogenization chamber opens into the ionization chamber.

[0037]

[0036] In one aspect of the present invention, the communication means includes a horizontal circular portion that partially closes the longitudinal end of the homogenization chamber, and the horizontal circular portion includes at least three radial grooves that communicate the homogenization chamber with the ionization chamber, or the communication means includes openings that radially penetrate the inner wall of the outer conductor and open into the homogenization chamber.

[0038] In one variation, the thruster further includes a solid, cylindrical structure, referred to as the "inner conductor," which extends along a longitudinal axis within the ionization chamber. In one aspect of the invention, the inner conductor has an outer surface made of graphite.

[0039] In one aspect of the invention, the inner conductor is comprised entirely of graphite. In another aspect of the invention, the inner conductor is comprised of a conductive material and has a graphite coating on its outer surface. In another aspect of the invention, the inner conductor is comprised of a conductive material and has a graphite tube on its outer surface. According to another aspect of the invention, the inner conductor is comprised of a conductive material and includes a graphite deposit on its outer surface. Under bombardment by plasma ions, graphite erodes less than conventional materials, such as aluminum, thereby extending the life of the thruster.

[0040] The present invention further relates to a method using the propulsion device of the present invention, said method comprising the following steps: - electrically connecting the portion made of conductive material to the negative terminal of a power source; - electrically connecting the outer conductor or another element of the propulsion device, excluding the screen, to the positive pole of the power source; - operating the power supply and the propulsion device.

[0041] The present invention also relates to an apparatus comprising a thrust device and a power supply device according to the present invention.

[0042] The present invention further relates to an apparatus, said apparatus comprising: an electron cyclotron resonance thruster extending at least partially along a longitudinal axis, the electron cyclotron resonance thruster comprising an outer conductor and an ionization chamber, the outer conductor and the ionization chamber extending longitudinally along said axis, the outer conductor laterally bounding the ionization chamber, the ionization chamber including a circular transverse opening with a diameter D, and a screen arranged coaxially with the longitudinal axis, the screen having a ratio of its largest transverse dimension D' to D between 3 and 15, the screen including a portion made of insulating material and a portion made of conductive material, the portion made of insulating material being configured to electrically insulate the portion made of conductive material from the remainder of the thruster; a power source, the negative electrode of which is electrically connected to the portion made of conductive material and the positive electrode of which is electrically connected to the outer conductor;

[0043] In one embodiment of the present invention, the device comprises a propulsion device including a magnetic field source and a body, and the positive pole of the power source is electrically connected to the magnetic field source or the body.

[0044] In one embodiment of the present invention, the apparatus comprises a propulsion device including an inner conductor, the positive pole of the power source being electrically connected to the inner conductor.

[0045]

[0044] Such a device makes it possible to apply a potential difference to a section of conductive material, resulting in the section being negatively polarized with respect to the outer conductor, the inner conductor, the magnetic field source, or the body of the thruster. When the device is operating and a plasma of ions and electrons is ejected, the negatively polarized coaxial screen pushes out the electrons trapped in the most divergent magnetic field lines, thereby redirecting these divergent electrons into an ejected particle beam. This increases the plasma flow ejected from the thruster.

[0046]

[0045] In one embodiment of the present invention, the device further includes a measurement unit and processing electronics configured to control the potential difference applied between the portion made of conductive material and the outer conductor or magnetic field source or body or inner conductor.

[0047] In the present invention, the outer conductor or inner conductor or magnetic field source or body is referred to as the reference.

[0048] The present invention further relates to a method for controlling a potential difference applied between a portion of conductive material and a reference using the device of the present invention, said method comprising the steps of: - measuring the potential difference between the part made of conductive material and a reference, called the effective potential difference, which is called the floating potential when the power supply 9 does not apply a potential difference, and the applied voltage when the power supply applies a potential difference; - calculating the difference between the effective potential difference and a predetermined set point; - if the difference exceeds a predetermined threshold, applying a potential difference of a value equal to the set value to the part made of conductive material by the power source, and the method returns to the first step; if the measured difference does not exceed the predetermined threshold, the method returns to the first step.

[0049] In one embodiment of the present invention, the set point is between 10 volts and 1 kilovolt, preferably between 100 volts and 500 volts, in absolute value. [Brief explanation of the drawings]

[0050] Other features and advantages of the invention will become apparent from the following description, which is given by way of example and not of limitation, and which should be read with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 shows, partially and diagrammatically, a longitudinal section of one propulsion device according to the invention. [Figure 2a]

[0051] FIG. 2a shows, partially and diagrammatically, a longitudinal cross-section of an open coaxial conductor of one propulsion device according to the invention. [Figure 2b]

[0051] Figure 2b shows, partially and diagrammatically, a longitudinal cross-section of an open coaxial conductor of one propulsion device according to the invention. [Figure 2c]

[0051] Figure 2c shows, partially and diagrammatically, a longitudinal cross-section of an open coaxial conductor of one propulsion device according to the invention. [Figure 2d] FIG. 2d shows, partially and diagrammatically, a longitudinal cross-section of an open coaxial conductor of one propulsion device according to the invention. [Figure 3a]

[0052] FIG. 3a shows, partially and diagrammatically, a longitudinal cross-section of the outer conductor and the inner conductor of one propulsion device according to the invention. [Figure 3b]

[0052] Figure 3b shows, partially and diagrammatically, a longitudinal cross section of the outer conductor and the inner conductor of one propulsion device according to the invention. [Figure 4a]

[0053] FIG. 4a shows, partially and diagrammatically, a longitudinal section of one propulsion device according to the invention. [Figure 4b]

[0053] Figure 4b shows, partially and diagrammatically, a longitudinal section of one propulsion device according to the invention. [Figure 5]

[0054] FIG. 5 shows, partially and diagrammatically, a longitudinal section of one propulsion device according to the invention. [Figure 6]

[0055] FIG. 6 shows, partially and diagrammatically, a longitudinal section of one propulsion device according to the invention. [Figure 7]

[0056] FIG. 7 shows, partially and diagrammatically, a longitudinal section of one propulsion device according to the invention. [Figure 8a]

[0057] FIG. 8a shows, partially and diagrammatically, a longitudinal cross-section of the open coaxial conductor and screen of one propulsion device according to the invention. [Figure 8b] FIG. 8b shows, partially and diagrammatically, a longitudinal cross-section of the open coaxial conductor and screen of one propulsion device according to the invention. [Figure 9]

[0058] FIG. 9 shows a diagram of one apparatus according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0051]

[0059] The dimensions of the elements shown in the figures do not correspond to actual dimensions or to the proportions of the dimensions. Furthermore, some of these elements are shown only symbolically, and elements with the same reference numerals in different figures represent identical elements or elements with the same function.

[0052]

[0060] An electron cyclotron resonance thruster according to the present invention is shown partially and diagrammatically in Figure 1. The thruster 10 extends at least partially along a longitudinal axis X and includes an open coaxial conductor 2, an ionization chamber 8, gas injection means 3, a microwave power injection device 4, a magnetic field source 1, and a coaxial screen 6.

[0053]

[0061] The principle of the electron cyclotron resonance satellite propulsion system will be briefly explained. A gas injection means 3 introduces gas into an ionization chamber 8. The gas is ionized by the addition of microwaves. The microwaves provide the electrical energy necessary to ionize the gas. These are generated, transmitted, and stored by a microwave power injection device 4. The signal frequency of the stored electrical energy is between 600 megahertz and 50 gigahertz. The electrical energy is transmitted to the propulsion gas according to the coaxial geometry described below or via a waveguide. A magnetic field source 1 applies a magnetic field to the plasma and its electrons. The electrons in the plasma undergo a rotational motion in a plane perpendicular to the magnetic field (quasi-transverse plane). The frequency of this rotational motion is determined by the value of the magnetic field. The value of the magnetic field and the frequency of the microwave signal are selected so that the electron rotation frequency is equal to the frequency of the microwave signal. This effectively deposits the power provided by the microwave signal in the plasma's electron population through a resonance phenomenon. The alternating electric field of the microwave signal accelerates the electrons in their rotational motion, increasing their kinetic energy in a quasi-transverse plane perpendicular to the magnetic field. Thus, the plasma is sustained with excellent energy efficiency. The generated electrons are ejected at high velocities due to the influence of magnetic forces and thermal expansion. The ejection of electrons creates an electric field that accelerates ions in the plasma, and the ejection of these ions at high velocities creates thrust.

[0054]

[0062] For the remainder of the thruster, the forward end of the thruster is defined as the longitudinal end of the thruster from which the propulsion gas is discharged. Thus, in the embodiment shown in Figure 1, the coaxial screen is located at the forward end of the thruster. Similarly, the aft end of the thruster is defined as the opposite longitudinal end. Thus, the microwave power generation device 41 is located at the aft end of the thruster.

[0055]

[0063] The thruster includes an open-type coaxial conductor 2 including an outer conductor 22 and an inner conductor 21. The outer conductor 22 has a generally hollow cylindrical shape coaxial with and extending longitudinally along a longitudinal axis X. The inner conductor 21 is disposed within the outer conductor 22 and has a solid cylindrical shape extending longitudinally along the axis X. The thruster includes a transverse plate 23, referred to as the aft plate, having a generally disk shape. The aft plate 23 contacts the aft longitudinal end of the outer conductor 22.

[0056]

[0064] The ionization chamber 8 comprises the volume existing between the outer conductor 22, the inner conductor 21, and the back plate 23. That is, the ionization chamber is bounded laterally by the outer conductor 22 and axially at its rear longitudinal end by the back plate 23. The ionization chamber has a lateral opening 24 at its front longitudinal end. This lateral opening 24 allows the propellant gas to escape. The lateral opening 24 is circular and has a diameter D.

[0057]

[0065] The outer conductor 22 includes an inner wall 221. As shown in FIGS. 1 and 2a, the inner wall has a cylindrical shape. Alternatively, the inner wall 221 has a frusto-conical shape, as shown in FIG. 2b. Alternatively, as shown in FIG. 2c, the inner wall 221 includes a cylindrical first portion 2211 and a frusto-conical second portion 2212 behind the ionization chamber 8. The second portion is aligned with the first portion, and the axis of rotation of the first and second portions coincides with the longitudinal axis X. In the above-described embodiments, the outer conductor is machined from a single block of material. In the embodiment shown in FIG. 2d, the outer conductor is fabricated from two separate portions. The outer conductor includes a second frusto-conical portion 225 connected to the cylindrical first portion 224, which extends longitudinally beyond the free longitudinal end 213 of the inner conductor 21. Alternatively, the inner wall shape can be defined by any surface of revolution. The outer conductor radially retains the propellant gas and forces it to eject axially through openings 24 .

[0058]

[0066] The outer conductor 22 is made of a conductive material. More specifically, in the present invention, the outer conductor is made entirely of graphite. Alternatively, the outer conductor is made of a conductive material and has a graphite deposition layer on the inner wall 221. The graphite is deposited using PVD (physical vapor deposition) technology. For example, the graphite is deposited by plasma or magnetron spraying of a graphite target. This technology can produce graphite with a thickness of 10 micrometers, which significantly improves the performance of the thruster. Alternatively, a graphite tube is inserted into the outer conductor made of a conductive material.

[0059]

[0067] The inner conductor 21 has a solid cylindrical shape and extends longitudinally along the axis X. The inner conductor includes an outer surface made of graphite. The inner conductor 21 may be entirely made of graphite, as shown in FIG. 3a. Alternatively, the inner conductor may be made of a conductive material and have a graphite coating on the outside. For example, the conductive material may be coated with a graphite deposit, deposited from a graphite target by magnetron spraying or plasma spraying. This technique can achieve graphite thicknesses of up to 10 micrometers, significantly improving thruster performance. As another example, as shown in FIG. 3b, the inner conductor includes a first portion 211 made of a conductive material and a second portion 212 made of graphite. The first portion 211 includes a first solid cylindrical body extending along the longitudinal axis X, which is axially extended by a cylindrical head having a diameter greater than that of the first cylindrical body. The second section 212 is a complementary sleeve for the first section, and the assembly of the first and second sections forms a solid cylinder extending along the X-axis within the ionization chamber. In this example, the top of the cylinder is covered with a graphite deposit not shown in Figure 3b.

[0060]

[0068] The outer conductor 22 and the inner conductor 21 form an open coaxial conductor 2 that allows microwaves to be stored in the ionization chamber. The microwaves are generated and supplied by a microwave power generator 4, which will be described later.

[0061]

[0069] The outer conductor 22 includes an outer wall 222 separated from an inner wall 221 by a lateral thickness 223. The outer conductor includes a homogenization chamber 32 formed in the lateral thickness 223. The homogenization chamber 32 extends longitudinally through a portion of the outer conductor 22. The homogenization chamber has a generally hollow cylindrical shape.

[0062]

[0070] The gas injection means 3 includes: at least one injection channel 31 extending radially through the outer wall 222 of the outer conductor 22 and through part of its lateral thickness 223, opening into the homogenization chamber 32; a homogenization chamber 32; - communication means configured so that the homogenization chamber opens into the ionization chamber.

[0063]

[0071] The communication means includes, for example, a horizontal circular portion 331 pressed against the rear plate 23. The horizontal circular portion 331 partially closes the rear longitudinal end of the homogenization chamber 32. The horizontal circular portion 331 is provided with at least three radial grooves that connect the homogenization chamber 32 with the ionization chamber 2. Alternatively, openings that radially penetrate the inner wall of the outer conductor 221 and open into the homogenization chamber are formed. In this second embodiment, the rear end of the homogenization chamber is directly closed by the rear plate 23 or the horizontal circular portion 331 that does not include grooves.

[0064]

[0072] The propellant gas is injected into the homogenization chamber through at least one injection channel 31. The gas propagates longitudinally and laterally within the homogenization chamber 32 and then enters the ionization chamber through the radial grooves in the transverse circular portion 331. The ionization chamber allows the gas to be injected into the ionization chamber in a controlled manner.

[0065]

[0073] The aft plate 23 comprises an insulating material that is relatively transparent to microwaves yet can withstand high thermal loads. For example, the aft plate may be made of ceramic or quartz. The aft plate allows the propellant gas to diffuse into the thruster opening 23 and receives a large portion of the heat flow from the plasma. The thruster includes a body 5 to which the aft plate 23 is integral.

[0066]

[0074] The body 5 of the thruster is made of a conductive material. The body 5 ensures the mechanical fixation of the various elements of the thruster and also allows the electrical connection between the microwave power injection device 4 and the open coaxial conductor 2.

[0067]

[0075] The microwave power injection device 4 includes a microwave power generator 41 and a transmission coaxial conductor 42. In an alternative configuration not described here, the microwave power injection device includes a waveguide 42.

[0068]

[0076] The microwave power generator 41 generates the microwaves required for the thruster's operation. It generates a signal of several tens of watts (W) to several kilowatts (kW) at a frequency of 2.45 GHz (Gigahertz). This signal is generated using a DC voltage of several tens of volts (V) and microwave oscillator technology. This signal is amplified by a solid-state amplifier or a field-effect amplifier (traveling wave tube, klystron).

[0069]

[0077] The transmission coaxial conductor 42 transmits the microwave signal from the generator 41 to the open coaxial conductor 2. The impedance of the transmission coaxial conductor 42 is 50 ohms. It includes an inner conductor 421 and an outer conductor 422 arranged concentrically with respect to each other, both of which are separated from each other by a concentric insulating layer 423 made of, for example, polytetrafluoroethylene (PTFE) or boron nitride (BN).

[0070]

[0078] The magnetic field source 1 includes a coil 12 or set of coils supplied with current. Alternatively, the magnetic field source may include a permanent magnet or set of permanent magnets. For a microwave signal with a frequency of 2.45 GHz, the magnetic field strength is adjusted to 875 gauss, and the electron cyclotron resonance region is located within 2 centimeters downstream from the aft plate 23. The magnetic field is high intensity at the magnetic field source 1 but rapidly attenuates at the thruster exit, creating a longitudinal magnetic field gradient. Furthermore, the magnetic field locally diverges at the ionization chamber exit, forming a magnetic nozzle that contributes to the acceleration of plasma ions.

[0071]

[0079] The propulsion device 10 of the present invention includes a coaxial screen 6. As shown in FIG. 1, the coaxial screen 6 extends perpendicular to the axis X. The coaxial screen 6 is fixed directly to the forward end of the outer conductor 22 by three screws 63. Alternatively, the coaxial screen 6 may be fixed to another axial position of the outer conductor 22. For example, the coaxial screen 6 is preferably fixed to a shoulder 226 of the outer conductor 22, as shown in FIG. 4b. Alternatively, as shown in FIG. 7, the coaxial screen 6 is fixed between the main body 5 and the magnetic field source 1. In this embodiment, the screen is held by three screws 63 passing through it, integrally securing the magnetic field source 1 to the main body of the propulsion device 5. Alternatively, as shown in FIG. 4a, the coaxial screen 6 is fixed to the magnetic field source 1. In this embodiment, the screen is fixed to the cover 13 by the screws 63. In another example (not shown), the screen is interposed between two covers 13 and 14 which hold the coil 12, and the covers 13, 14 and the screen 6 are fixed by screws along the longitudinal direction.

[0072]

[0080] The coaxial screen 6 may comprise a disk-shaped structure with a concave center, opening the ionization chamber opening 24, allowing the propellant gas to escape. Alternatively, as shown in FIG. 5, the coaxial screen may comprise a hollow cone-shaped structure with a truncated center.

[0073]

[0081] The coaxial screen 6 has a maximum lateral dimension D'. In the embodiment of FIG. 1, this maximum lateral dimension is the diameter D'. In the embodiment of FIG. 5, the maximum lateral dimension D' is the projection of the screen along the lateral direction. The maximum lateral dimension D' is selected so that the ratio D' / D is between 3 and 15. In the embodiment of FIG. 1, the ratio D' / D is 9. The figures do not quantitatively show this ratio. These figures are illustrative, as dimensions and dimensional ratios cannot be extracted.

[0074]

[0082] In the embodiment of FIG. 1, the coaxial screen 6 is made of an insulating material consisting of a mixture of glass fiber and epoxy resin. Alternatively, the screen may be made of Kapton®-type polyimide or a ceramic such as alumina or boron nitride. Alternatively, as shown in FIG. 8a, the screen may have a structure in which a portion of a conductive material 62 is covered with an insulating material 61. The conductive material 62 may be, for example, a metal reinforcement material onto which the resin 61 is poured. Alternatively, a film 61 made of an insulating material is fixed to a metal frame or structure 62. The film 61 may be, for example, a Kapton®-type polyimide. The screw 63 is made of an insulating material, for example, polyetheretherketone (PEEK) or polyetherketoneketone (PEKK).

[0075]

[0083] Alternatively, as shown in FIGS. 6 and 8b, the screen includes a section made of insulating material 61 and a section made of conductive material 62. The section made of insulating material 61 is configured to electrically insulate the section made of conductive material 62 from other elements of the propulsion system. The section made of insulating material 61 has, for example, the shape of a ring to which the conductive material 62 is attached and fixed. Alternatively, according to the embodiment of FIG. 6, the section made of insulating material has a frusto-conical shape and is attached in line with the outer conductor 22. The rotation axes of the section made of insulating material 61 and the outer conductor 22 coincide with the longitudinal axis X. The section made of insulating material extends longitudinally beyond the free longitudinal end of the inner conductor 21. The section made of conductive material 62 is fixed to the section made of insulating material 61. The section made of conductive material 62 is made of, for example, stainless steel, graphite, or aluminum. Insulating screws are used to fasten the shield 6 to the outer conductor 22 or other elements of the propulsion system 10. For example, if the fixing screw penetrates the conductive portion 62 and the insulating portion 61 and fits into the outer conductor 22, a screw made of polyetheretherketone (PEEK) or polyetherketoneketone (PEKK) is used. The conductive portion 62 is electrically connected to the negative pole of the power source 9, and the positive pole of the power source is connected to the outer conductor 22. When the power source is turned on, the conductive portion is polarized to the negative pole. The reference is set to the ground common to the electrically interconnected outer conductor 22, magnetic field source 1, and propulsion device body 5, or to any element of the propulsion device, such as the inner conductor 21.

[0076]

[0084] In the embodiment shown in Fig. 8b, the conductive part 62 covers the insulating part 61. The insulating part 61 is, for example, a reinforcement material and comprises an outer coating of conductive material, the latter constituting the conductive part. The coating is formed by depositing the conductive material, for example by PVD techniques. The conductive part 62 can also be joined to the insulating part 61. In these embodiments, the electrostatic potential of the conductive part is not controlled but is kept floating or is fixed according to the same characteristics as described in the previous paragraph with reference to Fig. 6.

[0077]

[0085] The invention also relates to a device 113 comprising a thrust device 10 of the invention and a power supply 9, as shown in FIG.

[0078]

[0086] The device 113 may further include elements as shown in Figure 9. Thus, the device 113 includes: an electron cyclotron resonance thruster 10 extending at least partially along a longitudinal axis, the electron cyclotron resonance thruster 10 comprising an outer conductor 22 and an ionization chamber 8, the outer conductor 22 and the ionization chamber 8 extending longitudinally along said axis, the outer conductor 22 laterally bounding the ionization chamber 8, the ionization chamber including a circular transverse opening 24 with a diameter D, and a screen 6 arranged coaxially with the longitudinal axis X, the screen 6 having a ratio of its maximum transverse dimension D' to D lying between 3 and 15, the screen 6 including a portion made of insulating material 61 and a portion made of conductive material 62, the portion made of insulating material 61 being configured to electrically insulate the portion made of conductive material 62 from the remainder of the thruster; a power source 9, the negative pole of which is electrically connected to the conductive material portion 62 and the positive pole of which is electrically connected to the outer conductor 22;

[0079]

[0087] Alternatively, the device 113 includes a propulsion device including a magnetic field source 1 and a body 5 , and the positive pole of the power source 9 is electrically connected to the magnetic field source 1 or the body 5 .

[0080]

[0088] Alternatively, the device 113 may include a propulsion device 10 having an inner conductor 21 to which the positive pole of the power source 9 is electrically connected.

[0081]

[0089] The device 113 further comprises a measurement unit 111 and processing electronics 112 configured to control the potential difference applied between the conductive material portion 62 and the outer conductor 22 or the magnetic field source 1 or the body 5 or the inner conductor 21.

[0082]

[0090] The outer conductor 22 or the inner conductor 21 or the magnetic field source 1 or the body 5 is called the reference.

[0083]

[0091] The present invention further relates to a method for controlling the potential difference applied between the conductive material portion 62 and a reference using the device 113 of the present invention, the method comprising the following steps: measuring the potential difference Vmes between the conductive material portion 62 and a reference, called the effective potential difference Veff, which potential difference is called the floating potential Vflott when the power supply 9 does not apply a potential difference, and called the applied voltage Vappl when the power supply applies a potential difference; - calculating the difference ε between the effective potential difference Veff and a predetermined set value Vcons; if the difference ε exceeds the predetermined threshold, applying a potential difference Vappl to the conductive material portion 62 by the power supply 9 with a value equal to the set value Vcons, and the method returns to the first step; if the measured value of the difference ε does not exceed the predetermined threshold, the method returns to the first step.

[0084]

[0092] The set point Vcons is between 10 volts and 1 kilovolt in absolute value, preferably between 100 volts and 500 volts.

Claims

1. 1. A satellite propulsion device (10) with an electron cyclotron resonance and magnetic nozzle extending at least partially along a longitudinal axis (X), comprising an outer conductor (22) and an ionization chamber (8), the outer conductor and the ionization chamber extending longitudinally along said axis, the outer conductor laterally bounding the ionization chamber, the ionization chamber including a circular transverse opening (24) having a diameter D, and a screen (6) arranged coaxially with the longitudinal axis (X), the screen (6) having a ratio of its maximum transverse dimension D' to D between 3 and 15, the screen (6) including a portion made of insulating material (61) and a portion made of conductive material (62), the portion made of insulating material covering the portion made of conductive material, or the screen entirely made of insulating material.

2. 2. A satellite propulsion device according to claim 1, characterized in that the portion made of insulating material (61) is configured to completely cover the portion made of conductive material (62), whereby the outer surface of the screen (6) is made of insulating material.

3. 3. A satellite propulsion device according to claim 1 or 2, characterized in that the screen (6) is attached to the outer conductor (22).

4. 3. A satellite propulsion device according to claim 1 or 2, comprising a magnetic field source (1) and a body (5), the screen (6) being attached to the magnetic field source (1), to the body (5), or between the magnetic field source (1) and the body (5).

5. 5. A satellite propulsion device according to claim 1, wherein the insulating material portion (61) or the screen (6) is made of a mixture of glass fibre and epoxy resin, or a mixture of carbon fibre and epoxy resin, or a Kapton-type resin or polyimide, or ceramic.

6. A satellite propulsion device according to any one of claims 1 to 5, characterized in that the screen (6) comprises a resin reinforcement and a polyimide film of the Kapton type.

7. 6. A satellite propulsion device according to claim 1, wherein the portion made of conductive material is a metallic reinforcement material.

8. A satellite propulsion device according to any one of claims 1 to 7, characterized in that the screen (6) comprises a disc shape with a concave center or a diverging shape, for example a truncated hollow cone or a nozzle shape.

9. A satellite propulsion device according to any one of claims 1 to 8, characterized in that the outer conductor (22) includes an inner wall (221) made of graphite.

10. 10. A satellite propulsion device as recited in claim 9, wherein the outer conductor (22) separates an inner wall (221) and an outer wall (222) by a lateral thickness (223) and includes a homogenization chamber (32) formed within the lateral thickness (223), the homogenization chamber extending longitudinally through a portion of the outer conductor and having a generally hollow cylindrical shape.

11. at least one injection channel (31) passing radially through said outer wall (222) and partly through said lateral thickness (223) of said outer conductor (222) and opening into said homogenization chamber (32); said homogenization chamber (32), A satellite propulsion device according to claim 10, characterized in that it comprises gas injection means (3) including communication means arranged so that said homogenization chamber (32) opens into said ionization chamber (8).

12. 12. The satellite propulsion device of claim 11, wherein the communication means includes a transverse circular portion (331) partially closing a longitudinal end of the homogenization chamber, the transverse circular portion including at least three radial grooves communicating the homogenization chamber with the ionization chamber, or the communication means includes openings radially penetrating an inner wall (221) of the outer conductor and opening into the homogenization chamber.

13. 13. A satellite propulsion device according to any one of claims 1 to 12, further comprising an inner conductor (21) having a solid cylindrical shape, said inner conductor extending along a longitudinal axis (X) in said ionization chamber and including an outer surface made of graphite.

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